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Abstract

Background: The presence of two or more pathogenic sarcomere mutations in patients with hypertrophic cardiomyopathy (HCM) has been reported to be associated with early disease onset, particularly marked left ventricular (LV) hypertrophy, and advanced heart failure.

Objective: The aim of the study was to clarify the relationship between multiple disease-causing sarcomere mutations and major cardiovascular outcomes in a large HCM cohort.

Methods and Results: Between June 1, 1995, and January 2015, 1104 probands with a diagnosis of HCM were routinely referred for systematic sarcomeric mutational screening at a single HCM center. Pathogenic mutations were identified in 273 (25%). Of these patients, 10 (3.6%) were identified with double/compound sarcomere mutations. They were mostly male (70%), presented at an average age of 33±13 years (range, 21-58), with an average maximal wall thickness of 17 mm (range, 13-26). Of the 9 patients who had a cardiac MRI, 8 (88%) had late gadolinium enhancement (LGE), none of which were considered to be extensive (>20% of LV myocardium).

Over a mean follow up of 17.4 ±14 years (range, 3-48 years) there were no sudden cardiac death events. Adverse cardiovascular events or severe disease progression occurred in 4 (40%) patients, with an event rate of 3.4 per 100 patient-years follow up including: 2 (20%) with stroke, 3 (30%) with progression to end-stage HCM (EF<50%), and 1 (10%) with progression to New York Heart Association III/IV symptoms. One patient had myectomy for obstructive symptoms, while none required cardiac transplantation. Three (30%) patients had implantable cardioverter-defibrillator (ICD) for primary prevention. However, over a mean follow-up of 6 years (range 1-14 years), no ICD discharges were documented.

Conclusion: These observations do not support the hypothesis that double (or compound) mutations confer a gene dosage effect in HCM, nor is it associated with an adverse prognosis. Mutation analysis has proven imprecise in predicting the phenotype or prognosis for patients with HCM, suggesting that genome-wide association studies and gene expression profiling may be needed for better understanding of its utility in the management of HCM patients.